Light polarizer

ABSTRACT

A polarizer comprising at least one subwavelength optical microstructure that includes linear prisms, and wherein said microstructure is partially covered with a light-transmissive inhibiting surface.

RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.10/728,128, filed Dec. 4, 2003, which is a continuation-in-part of U.S.application Ser. No. 09/927,781, filed on Aug. 10, 2001, which claimsthe benefit of U.S. Provisional Application No. 60/225,246, filed onAug. 15, 2000. The entire teachings of the above applications areincorporated herein by reference.

BACKGROUND OF THE INVENTION

Sunlight is typically regarded as unpolarized light. In order to reducethe glare on reflected light, glass lenses have incorporated polarizingelements. The light is typically polarized by introducing a polarizationfilm to each lens element to produce polarized light wherein theimpinging light is divided into reflected, absorbed and transmittedpolarized light beams by the polarizing lens elements. Coatings havealso been applied to lens elements in order to produce a mirroredappearance for the lenses and to decrease transmission of visible lightin order to reduce the associated glare.

SUMMARY OF THE INVENTION

In one embodiment, the present invention is a polarizer comprising atleast one subwavelength optical microstructure that includes linearprisms, wherein said microstructure is partially covered with alight-transmissive inhibiting surface.

In another embodiment, the present invention is a polarizer comprising asubstrate having a plurality of linear prisms formed thereon, the linearprisms having a partially metalized surface.

In another embodiment, the present invention is a method of forming apolarizer, comprising partially covering a subwavelength opticalmicrostructure with light-transmissive inhibiting surface, whereinoptical microstructure includes linear prisms.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of various embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1 is partial isometric view of a polarizing film utilizing moth-eyestructures in accordance with the present invention.

FIG. 2 is a side view of a subwavelength optical microstructure.

FIG. 3 is a partial isometric view of a polarizing film utilizingmoth-eye structures in accordance with the present invention.

FIG. 4 is a partial isometric view of a polarizing film utilizingmoth-eye structures in accordance with the present invention.

FIG. 5 is a partial isometric view of a polarizing film utilizingmoth-eye structures in accordance with the present invention.

FIG. 6 is a partial isometric view of a polarizing film utilizing linearprisms in accordance with the present invention.

FIG. 7 is a partial isometric view of a polarizing film utilizingmodified moth-eye structures in accordance with the present invention.

FIG. 8 is a partial isometric view of a polarizing film utilizing linearprisms having a transparent coating thereon in accordance with thepresent invention.

FIG. 9 is a side view of an apparatus for metalizing polarizing film inaccordance with the present invention.

FIG. 10 is a partial isometric view of a polarizing film utilizingmoth-eye structures which have both sides of the peaks metalized inaccordance with the present invention.

FIG. 11 is a partial isometric view of a polarizing film utilizinglinear prisms which have both sides of the peaks metalized in accordancewith the present invention.

FIG. 12 is a partial isometric view of a polarizing film utilizingmultiple moth-eye structures in accordance with one embodiment of thepresent invention.

FIG. 13 is a partial isometric view of a polarizing film utilizingmultiple moth-eye structures in accordance with another embodiment ofthe present invention.

FIG. 14 is a partial isometric view of a polarizing film utilizingmultiple moth-eye structures in accordance with yet another embodimentof the present invention.

FIG. 15 is a partial isometric view of a polarizing film utilizingmultiple moth-eye structures in accordance with another embodiment ofthe present invention.

FIG. 16 is a partial isometric view of a linear prism having apolarizing film on one surface.

FIG. 17 is an isometric view of a cube-corner prism having a polarizingfilm on one surface.

FIG. 18 is a partial isometric view of a lens having a polarizing filmon one surface.

FIG. 19 is a partial isometric view of a surface relief diffuser havinga polarizing film on one surface.

FIG. 20 is a side view of a tool used to form linear prisms for use inpolarizing films in accordance with the present invention.

FIG. 21 is a side view of the tool of FIG. 20 forming the linear prisms.

FIG. 22 is a partial isometric view of a liquid crystal displayutilizing a polarizing film in accordance with the present invention.

FIG. 23 is a partial isometric view of a liquid crystal displayutilizing a polarizing film in accordance with the present invention.

FIG. 24 is a partial isometric view of a color filter utilizing apolarizing film in accordance with the present invention.

FIG. 25 is a side view of a moth-eye structure having a conductivesurface and a conductive coating thereon for forming a polarizing film.

FIG. 26 is a side view of a polarizing film utilizing a moth-eyestructure in which a conductive surface and a conductive coating areprovided in the valleys of the moth-eye structure.

FIG. 27 is a side view of a polarizing film utilizing a moth-eyestructure in which a conductive surface is provided on peaks of themoth-eye structure.

FIG. 28 is a side view of a polarizing film utilizing a moth-eyestructure in which conductive particles are provided in the valleys ofthe moth-eye structure.

FIG. 29 is a side view of a polarizing film utilizing a moth-eyestructure in which conductive filler is provided in the valleys of themoth-eye structure.

FIG. 30 is a side view of a polarizing film utilizing a moth-eyestructure in which an opaque filler is provided in the valleys of themoth-eye structure.

FIG. 31 is a side view of a tool used to form a moth-eye structure inwhich particles are disposed in a resin used to form the moth-eyestructure.

FIG. 32 is a side view of a moth-eye structure formed by the toolillustrated in FIG. 31 in which particles are disposed in the peaks ofthe moth-eye structure.

DETAILED DESCRIPTION OF THE INVENTION

A description of various embodiments of the invention follows. FIG. 1illustrates an embodiment of a polarizing film, generally designated asreference numeral 10. A subwavelength optical microstructure, such as alinear moth-eye structure 12, is formed on a substrate 14. Moth-eyestructures are explained in more detail in U.S. application Ser. No.09/438,912, now issued as U.S. Pat. No. 6,356,389 on Mar. 12, 2002,filed Nov. 12, 1999, now issued the teachings of which are incorporatedherein in their entirety. In one embodiment, the moth-eye structure 12is formed from the same material as the substrate 14. The moth-eyestructure can be formed, for example, through embossing, molding, orcasting. In another embodiment, the moth-eye structure 12 is formed froma material having a different index of refraction than the substrate 14.The substrate 14 can include light-transmissive materials such asplastics. In one manufacturing technique, the substrate 14 is relativelysoft such that the moth-eye tool penetrates the substrate so excessresin layer is not present.

As shown in FIG. 2, the moth-eye structure 12 applied in one embodimenthas an amplitude (A) of about 0.4 micrometers and a period (P) of lessthan about 0.2 micrometers. The structure is sinusoidal in appearanceand can provide a deep green to deep blue color when viewed at grazingangles of incidence. If the period (P) is made to be about 180 nm orless, this color will not be present. In one embodiment, the amplitudeis about three times the period to provide a three to one aspect ratio.

The moth-eye structure 12 provides anti-reflection properties to thepreviously smooth light entrance surface of the substrate even atentrance angles that are near grazing incidence. The moth-eye structureis more effective than standard thin film anti-reflection coatings atwide angles of incidence especially angles of incidence beyond 30degrees up to 80 degrees. This characteristic can cause many types ofoptical microstructure films including linear prism films to processlight very differently than the standard linear prism collimating filmswhich have smooth entrance surfaces with or without standardanti-reflection thin film (vacuum deposited or liquid applied) coatings.The addition of the moth-eye structures helps to more efficientlyrecycle light and also redirects the normally reflected grazing angleincidence rays into the optical microstructure (such as linear prisms)sheet where the rays are refracted, reflected or retroreflecteddepending on the respective angles of incidence. This moth-eyeimprovement concept can be added to many types of brightness enhancementfilms (BEF). An advantage is that functional optical microstructures canbe applied to both sides of a film or substrate.

A moth-eye anti-reflection surface is one in which the reflection oflight is reduced by the presence of a regular array of smallprotuberances covering the surface. The spacing of the protuberances isless than the wavelength of light for which anti-reflection is sought. Amoth-eye surface can be understood in terms of a surface layer in whichthe refractive index varies gradually from unity to that of the bulkmaterial. Without such a layer, the Fresnel reflection coefficient at aninterface of two media is equal to ((n₁−n₂)/(n₁+n₂))², where n₁ and n₂are the refractive indices of the media. However, if there is a gradualchange of index, net reflectance can be regarded as the result of aninfinite series of reflections at each incremental change in index.Since each reflection comes from a different depth from the surface,each has a different phase. If a transition takes place over an opticaldistance of λ/2, all phases are present, there is destructiveinterference and the reflectance falls to zero.

When the height of the protuberance (h) is significantly less than thewavelength (λ), the interface appears relatively sharp and thereflectance is essentially that of a discontinuous boundary. As theratio of h/λ increases, the reflectance decreases to a minimum value atabout h/λ=0.4. Further increases in h/λ show a series of successivemaxima and minima, but the value does not again approach that of a sharpinterface. The details of the curve shown in FIG. 2 vary depending onthe profile of the change of the index of refraction, but if thethickness is of the order of half a wavelength or more the reflectanceis considerably reduced. The spacing of the protuberances should besufficiently fine to avoid losses by diffraction. Preferably, it shouldbe less than the shortest wavelength involved divided by the refractiveindex of the material.

It is important that the spacing P between the peaks of theprotuberances on the moth-eye surface is sufficiently small that thearray cannot be resolved by incident light. If this is not the case, thearray can act as a diffraction grating and, although there may well be areduction in the specular reflection (zero order), the light is simplyredistributed into the diffracted orders. In other words, P is less thanλ for normal incidence and d is less than λ/2 for oblique incidence iffor reflection only, and that d is less than λ/2n in the case oftransmission where diffraction inside the material is suppressed.

For a given moth-eye surface, where the height of the protuberances is hand the spacing is d, the reflectance is expected to be very low forwavelengths less than about 2.5h and greater than d at normal incidence,and for wavelengths greater than 2d for oblique incidence. In oneembodiment, the spacing is as close as possible, and the depth as greatas possible, in order to give the widest possible bandwidth. Forexample, a h/d ratio can be about three.

The moth-eye effect should not be confused with that of reducing thespecular reflectance by roughening. Roughness merely redistributes thereflected light as diffuse scattering and degrades the transmittedwavefront. With the moth-eye structure, there is no increase in diffusescattering, the transmitted wavefront is not degraded and the reductionin reflection gives rise to a corresponding increase in transmission.

The moth-eye structure 12 has many advantages. There is no extra coatingprocess necessary. The structure can be transferred to the sheet by apressure molding process, such as with a Fresnel structure. Thereflection reduction does not depend on the wavelength. There is only alower limit (on the ultraviolet side of the spectrum) set by thestructure period. If the wavelength is too small compared to the period,the light is diffracted. In regard to angular dependence, withconventional anti-reflective coatings, the transmission curve shiftswith the light incidence angle. With the moth-eye structure, thecritical wavelength for diffraction shifts to higher values, but thereare no changes above this wavelength. Another advantage for moth-eyestructures is that there can be no adhesion problems between lens andgradient layer because it can be one bulk material. From a high incidentangle, the surfaces can appear blue or violet.

In one embodiment of forming a moth-eye structure, the structure isfirst produced on a photoresist-covered glass substrate by a holographicexposure using an ultraviolet laser. A suitable device is available fromHolographic Lithography Systems of Bedford, Mass. 01730. An example of amethod is disclosed in U.S. Pat. No. 4,013,465, issued to Clapham et al.on Mar. 22, 1977, the teachings of which are incorporated herein byreference. This method is sensitive to changes in the environment, suchas temperature and dust, and care must taken. The structure is thentransferred to a nickel shim by an electroforming process. In oneembodiment, the shims are about 300 micrometers thick or less.

The moth-eye structures can be made one dimensional in a grating typepattern. In this embodiment, the structure has a nearly rectangularprofile, which means they have no gradient layers, but more of a onelayer anti-reflective coating with a lowered refractive index in thestructure region. Control of the grating depth is important as iscontrol of thickness for the evaporated layers. Control of depth andthickness is achieved by maintaining uniformity of beam exposure,substrate flatness and exposure time.

A two-dimensional structure is formed by two exposures with a linearsinus-grid, turned by 90 degrees for the second exposure. A third typeof structure is formed by three exposures with turns of 60 degrees toprovide a hexagonal or honeycomb shape.

In one embodiment, the material which forms the moth-eye structure 12 issubstantially transparent as formed. Exemplary materials include athermoplastic or thermoset, such as polymethalmythacrylate,polyurethane, or polycarbonate. In one embodiment, ultraviolet curedthermoset materials which have a low viscosity prior to curing providethe preferred replication fidelity. The moth-eye structure 12 caninclude valleys 16 and peaks 18. The pitch P, or distance betweenvalleys 16, in one embodiment, is less than or equal to about 250 nm.The amplitude A, or vertical distance from peak 18 to valley 16, in oneembodiment, is greater than or equal to about 250 nm for visiblewavelength light.

In one embodiment, at least part of the surface of the moth-eyestructure 12 includes a light-transmissive inhibiting surface, such as areflective or diffuse surface 20. As shown, the surfaces 20 are spacedapart and substantially parallel. In one embodiment, the reflectivesurface 20 is formed from a metalized coating, such as aluminum or thelike. The diffuse surface, in one embodiment, includes an engineeredsurface relief diffuser such that light incident upon the surface isredirected in transmission and by reflection. An example of suitablediffusers is disclosed in U.S. Pat. No. 5,600,462, issued to Suzuki, etal. on Feb. 4, 1997, the teachings of which are incorporated herein byreference. Another example of a suitable relief diffuser is disclosed inan article entitled “Holographic surface-relief microstructures forlarge area applications” by V. Boerner, et al. of Fraunhofer Institutefor Solar Energy Systems ISE, Oltmansstr. 5, 79100 Freiburg, Germany,which was presented in a conference held in Copenhagen, Denmark from May28-30, 2000, the teachings of which are incorporated herein byreference.

It is known that closely spaced parallel electrical conductors can beused to polarize electromagnetic waves. The conductors reflect andabsorb waves that are polarized in a plane that is parallel to thelength of the conductors. A wave that is polarized in a planeperpendicular to the length of the conductors passes through theconductors with little transmission loss.

As shown in FIG. 3, the polarizing film 10 reflects and absorbs lightrays, such as light ray 22, which travel in a plane 24 parallel to thefilm. More particularly, plane 24 is parallel to valleys 16, peaks 18,and surfaces 20. As shown in FIG. 4, if light ray 22 were traveling in anon-parallel plane, for example, plane 26, the light ray would passthrough the film 10 with little transmission loss. In this manner, onlylight rays which are substantially perpendicular to the valleys 16,peaks 18, and surfaces 20 are allowed to pass through the film 10. Theamount of light reflected or diffused is dependent upon the reflectionand transmission properties of surface 20. Thus, a simple and relativelyinexpensive polarizing film has been discovered.

FIG. 5 illustrates the same concept of FIGS. 3 and 4. An incomingrandomly polarized light wave 19 is polarized. More particularly, thefilm 10 reflects the component 23 of the light wave 19 which lies inplane parallel to the surfaces 20 and allows transmission of thecomponent 21 of the light wave perpendicular to the surfaces 20.

FIG. 6 illustrates another embodiment of the polarizing film 10 whichincludes linear prisms 28 formed on substrate 14. In one embodiment, thelinear prisms 28 are isosceles triangles with the height greater thanthe base with the pitch as described before. As illustrated in FIG. 7,yet another embodiment of a polarizing film 10 is illustrated. Amoth-eye type structure 30 having a flat top 32 having surface 20thereon. In this embodiment, the light which is reflected back canreflect back in a direction consistent with the angle of incidenceequaling the angle of reflection from flat top 32. If surface 20 ismetalized and combined with a surface relief diffuser or structuredsurface as shown in FIG. 19, the surface serves as a type of anti-glaresurface. Directional light, such as from an overhead light fixture, isreflected at a defined angle(s) away from the surface. Light passingthrough the polarizer is viewed without interference from the reflectedlight. Applications range from a window film to a computer monitor film.Other shapes of the polarizing film, or combinations of the disclosedshapes of the structures, are contemplated herein. Further, thesubstrate 14 can be formed from the same material as the structurehaving surface 20.

FIG. 8 illustrates a transparent coating 34 formed over linear prisms 28to protect the surface 20. Transparent coating 34 can be formed over anyof the disclosed embodiments. The shape of this structure reflectsambient light 36 away in a controlled direction and is one form ofconstruction that can be used as an anti-glare light redirection film aswell as a polarizing film. This structure can also be used to create ananti-counterfeit document feature because when superimposed upon adocument with an optically clear adhesive, the document is easily viewedin specific directions. However, when the document is photocopied, thecopy is darker as a result of much of the light being reflected. Otherindicia, such as logos and water marks, can be added into the film, forexample, by removing a portion of the moth-eye structure or patternmetalizing. In one embodiment, laser etching is used to remove thestructure in the moth-eye tooling without effecting the transmission ofthe film 10.

FIG. 9 illustrates one embodiment of the manufacturing process forproducing surface 20. In this embodiment, the optical microstructure iswrapped about a cylinder 38, which can be about 5 centimeters indiameter. A metal source 40, such as aluminum, is positioned about 19centimeters inches from the center of cylinder 38. A baffle or mask 41,disposed between the cylinder 38 and the metal source 40, prevents themetal from covering the entire microstructure. The baffle or mask 41 canbe sized sufficiently to block the surface of the microstructure fromthe metal source 40 except in area “A”. This arrangement is positionedwithin a bell jar vacuum. Angle α in this embodiment is about 7.5degrees. In one embodiment, the microstructure included a moth-eyestructure and it was found that in area “A”, the moth-eye structure hadthe optimal amount of metalization on one side of the peaks 18. Thecylinder 38 can be rotated such that the entire moth-eye structure iscoated at area “A”. In alternative embodiments, as illustrated in FIGS.10 and 11, both sides of the peaks 18 are coated by setting the coatingfeatures to allow the coating to impact the surface when coming fromdifferent angles. The position of the metal source 40 and masks can beadjusted to created a desired coated area.

In alternative embodiments, the entire microstructure is metalized forexample, with aluminum. More metal is deposited on the peaks than on thewalls and valleys because of the various directions the metal impactsthe microstructure. The microstructure is then etched with a caustic fora defined period of time to remove the thinner metal layer while leavingthe metal on the peaks.

FIG. 12 illustrates another embodiment of a polarizing film 10. It isknown that essentially 0% of the light component which is perpendicularto the linear moth-eye rows is reflected at each moth-eye boundarybecause the moth-eye acts as an anti-reflection surface in thisdirection. It is further known that approximately 4% of the lightcomponent which is parallel to the linear moth-eye, for example, lightray 22 in plane 24, is reflected at each linear moth-eye boundarybecause the light wave sees a flat surface rather than a moth-eyesurface. Thus, with enough moth-eye layers, substantially all of thelight component which is parallel to the linear moth-eye structures isreflected and only the light perpendicular to the moth-eye structuresare transmitted therethrough to create a linear reflecting polarizer.Other structures can be stacked on one another to create a polarizer,such as a linear prism structure (FIG. 6) or a modified type moth-eyestructure (FIG. 7).

FIG. 13 illustrates multiple moth-eye structures 12 stacked on oneanother to form a polarizing film 10. In one embodiment, approximately40 layers or 80 surfaces can be used to achieve effective polarizationof the light, which polarizes approximately 96% of the light passingthrough the film.

FIG. 14 illustrates another embodiment of a stack moth-eye structure 12which forms a polarizing film 10. In this embodiment, a fill layer 44 isprovided between each moth-eye structure 12 to vary the reflectionproperties by changing the refractive index of the moth-eye structurerelative to the substrate 14 and fill layer. Fill layer 44 can includelow index of refraction materials such as silicone based andfluoropolymer based materials.

For optimal performance, n1 is greater than n2. In one embodiment, n1 isgreater than n2 by 0.5 units or more to reduce the number of layerswhich can be used to achieve effective polarization of the light. Thenumber of layers is reduced because the greater the index of refraction,the more light is reflected at each boundary. In one embodiment, n1 isapproximately 1.59 and n2 is approximately 1.42 with a delta of 0.16. Inthis case, approximately 100 layers or 200 surfaces can be used toachieve effective polarization of the light.

FIG. 15 illustrates another embodiment of a polarizing film 10. Acoating 34, such as a transparent coating, can be applied over surfaces20 to protect the same. Moth-eye structures 12 can be added to eithersurface 46 and 48, or both, to improve the light transmission of thefilm 10. In the embodiment shown in FIG. 15, a moth-eye structure 12 hasbeen added to both surfaces 46 and 48. The location of the surface 20can be defined such that it will act as an anti-glare surface byreflecting unwanted light away from a display. This structure furtheracts as a contrast enhancing film because of the anti-reflection,polarization and dark line pattern created by the surface 20.

FIGS. 16, 17, 18, and 19 illustrate exemplary applications for thepolarizing film 10. FIG. 16 illustrates the protective coating 34 formedinto a linear prism to form a transparent polarizing linear prismcollimating film. In one embodiment, the linear prisms have a height inthe range of between about 10 and 200 micrometers and a pitch in therange of between about 20 and 400 micrometers. An example of suitablelinear prisms is disclosed in U.S. Pat. No. 4,260,220 issued toWhitehead on Apr. 7, 1981, the teachings of which are incorporatedherein by reference. FIG. 17 illustrates the protective coating 34formed into a cube-corner prism to form a transparent polarizingcube-corner film. In one embodiment, the cube-corner prisms can have aheight in the range of between about 20 and 200 micrometers and a pitchin the range of between about 50 and 500 micrometers. Examples ofsuitable cube-corner prisms are disclosed in U.S. Pat. No. 3,684,348,issued to Rowland on Aug. 15, 1972, the teachings of which areincorporated herein by reference. FIG. 18 illustrates the protectivecoating 34 formed into a lens. Many types of polarizing lenses can beformed including lenticulars, linear bar lenses, single lenses, lensarrays, etc. FIG. 19 illustrates the protective coating 34 formed intothe shape of a surface relief diffuser for use in applications such asfront and rear projection screens.

FIGS. 20 and 21 illustrate a method of manufacturing subwavelengthlinear prisms having a different index of refraction than the supportingsubstrate. FIG. 20 is a side view of a drum that is ruled to form a tool50 having linear prisms at approximately the pitch of a moth-eyestructure. In one embodiment, this pitch is about 250 nm. Resin 52 iscast onto a relatively soft substrate 54, such as urethane or vinyl,which allows the linear prism tips 55 to penetrate the substrate leavingresin in subwavelength size (FIG. 21). In this embodiment, the resin 52has an index of refraction different than substrate 54.

In any of the disclosed embodiments, if surface 20 is metalized orincludes a conductive material, it can be used as a narrow conductingpath for use in products such as liquid crystal displays. Thus, the samefilm 10 can be used to polarize the light and serve as a conductingpath. Additionally, the channels, such as the valleys 16 of the moth-eyestructures, can act as alignment grooves for the liquid crystalmaterial, as illustrated in the embodiment of FIG. 22.

Generally, in one embodiment, a pair of moth-eye structures 12 havingconductive surfaces 20 for polarizing incoming random light arepositioned 90 degrees relative to one another. A passivation coating orlayer 56, such as an oxide layer, can be formed on the moth-eyestructure 12 to protect the structure against contamination and toincrease electrical stability. The moth-eye channels or valleys 16 actas alignment grooves for the liquid crystals 58 which turn through 90degrees with the material directly adjacent the valleys 16 beingsubstantially parallel thereto. As understood in the art, when anelectric current is carried, for example, by surfaces 20, the liquidcrystals 58 are aligned such that light polarized by a polarizer in afirst direction is blocked by the adjacent polarizer, which is 90degrees offset. With no electric current, the liquid crystals arealigned as illustrated in FIG. 22 such that the light's plane ofvibration twists through a right angle so light passes through theadjacent polarizer.

In the embodiment of FIG. 23, layer 60 is made using existing standardtechnology and includes a passivation coating 56 formed over the entiresurface. A plurality of brushed alignment channels 62 are used to alignthe liquid crystals 58. A polarizer 10, such as a moth-eye structure 12having surfaces 20, can be placed on the outside surface for polarizingincoming light. The other polarizer (shown on top in FIG. 23) can besimilar to the polarizers as shown in FIG. 22. Thus, in accordance withthe present invention, the expensive secondary step of brushingalignment channels can be beneficially avoided.

FIG. 24 illustrates a moth-eye 12 polarizer in accordance with thepresent invention, used in conjunction with a resonance structure 64,such as an Aztec structure developed by Dr. Jim Cowan, to provide a highcontrast color filter. Unpolarized light 66 is polarized by the moth-eyestructure 12 such that polarized light 68 impinges upon the resonancestructure 64. Only light of a predetermined wavelength is reflected bythe resonance structure at a given location to produce a high contrastoutput wavelength 70.

The polarizing film of the present invention can be used in a wide rangeof applications including sunglasses, LCD displays, windows, andsecurity documents. The polarizing film can be made very thin and lightin weight. The thickness of the film can be as small as one wavelengthof light. In one embodiment, the thickness of the moth-eye structurecarried on a substrate is in the order of 12.7 micrometers or greater(0.0005 inches or greater).

Also, the materials used can be very temperature stable relative to thematerial used to make traditional polarizing films. Traditionalpolarizers are made by aligning microscopic crystals in a suitable base.A traditional polarizer typically performs in a range of 25 to 40%efficiency because of absorption losses. The polarizer of the presentinvention achieves a near 50% efficiency with the only losses occurringfrom absorption within the clear polymers used to construct thepolarizer and imperfections in the reflective coating process.

Also, because the approximately 50% or less of light that is reflectedfrom the coated surfaces is not absorbed, it is available to be recycledback through the new polarizer material. Thus, an efficient polarizer isprovided in accordance with the present invention.

FIGS. 25 and 26 illustrate an embodiment for forming a reflective orabsorptive polarizing film 10. A subwavelength optical microstructure,such as a moth-eye structure or film 12, is cast or otherwise provided.A conductive or metal surface or coating 72, which can have a thickness74 of about 500 angstroms in a particular embodiment, can be formed,such as by vacuum metallization or other suitable techniques, on themoth-eye film 12. A conductive coating 76 can be electroplated orotherwise formed on the conductive surface 72. The conductive surface 72can be used to grow the conductive coating 76. The conductive coating 76and surface 72 can be removed from the moth-eye peaks 18 leaving valleys16 fully conductive. The conductive coating 76 and surface 72 can beremoved from the peaks 18 by caustic chemical etching techniques,mechanical brushing, skiving, or other suitable techniques. Asubstantially transparent coating 34 can be provided to protect thepolarizing film 10.

In another embodiment of a polarizing film 10 as illustrated in FIG. 27,a soluble coating can be applied to the valleys 16 of the moth-eye film12 prior to forming the conductive surface 72 on the film. This allowsthe conductive surface 72 to be rinsed off the valleys 16 leaving theconductive surface on the peaks 18. A substantially transparent coating34 can be provided on the film 10.

In other embodiments of a polarizing film 10, a moth-eye film 12 can becast or otherwise provided as illustrated in FIG. 28. A plurality ofconductive particles 78 can be provided in the moth-eye valleys 16 whileleaving the peaks 18 exposed. In one embodiment, the particles 78 caninclude nano particles. In other embodiments, the particles 78 caninclude about 0.2 micrometer or smaller size metal particles, such assilver (Ag), aluminum (Al), titanium dioxide (TiO₂), or other suitablematerials. In a particular embodiment, a magnet can be used to pull theparticles 78 into the valleys 16, and excess particles can be removedleaving the peaks 18 exposed. A substantially transparent coating 34 canbe provided on the polarizing film 10.

In another embodiment of a polarizing film 10 illustrated in FIG. 29, aconductive filler 80, which can include conductive fibers, can beprovided in the valleys 16 of a moth-eye film 12. In a particularembodiment, the conductive filler 80 can be brushed into the valleys 16and excess filler removed so that the peaks 18 are substantially clean.A substantially transparent coating 34 can be provided on the polarizingfilm 10.

FIG. 30 illustrates another embodiment of a polarizing film 10 in whichan opaque filler 82, which can include opaque fibers, is provided in thevalleys 16 of a moth-eye film 12. In a particular embodiment, the filler82 can be brushed or coated into the valleys 16 and excess fillerremoved so that the moth-eye peaks 18 are clean. A substantiallytransparent coating 34 can be provided on the polarizing film 10.

In another embodiment, a resin 84, which can be conductive, is cast on alinear moth-eye mold 11, as illustrated in FIG. 31, to form moth-eyefilm 12. A plurality of particles 86 can be provided in resin 84 thatsink to the bottom of the mold 11, which forms the peaks 18 of theresulting moth-eye film 12. In a particular embodiment, the particles 86can be conductive. When the moth-eye film 12 is cured and removed, asillustrated in FIG. 32, the particles 86 are thus formed in at leastsome of the peaks 18. A substantially transparent coating 34 can beprovided on the polarizing film 10.

While this invention has been particularly shown and described withreferences to various embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

1. A polarizer, comprising: at least one subwavelength optical microstructure, said microstructure being partially covered with a light-transmissive inhibiting surface; and a coating disposed over at least part of the optical microstructure and the inhibiting surface.
 2. The polarizer of claim 1, wherein the coating is collimating.
 3. The polarizer of claim 2, wherein the coating is formed into at least one linear prism.
 4. The polarizer of claim 1, wherein the coating is formed into a cube-corner prism to form a transparent polarizing cube-corner film.
 5. The polarizer of claim 1, wherein the coating is formed into a lens.
 6. The polarizer of claim 1, wherein the coating is formed into a surface relief diffuser.
 7. The polarizer of claim 1, wherein the optical microstructure include moth-eye structures, linear prisms, or a combination thereof.
 8. The polarizer of claim 1 wherein the light-transmissive inhibiting surface includes reflective surface.
 9. The polarizer of claim 1 wherein the light-transmissive inhibiting surface is a metalized coating.
 10. The polarizer of claim 1, wherein the optical microstructure includes a flat surface upon which the light-transmissive inhibiting surface is disposed.
 11. The polarizer of claim 1, wherein the optical microstructure includes peaks and valleys, wherein the light-transmissive inhibiting surface is primarily disposed on the peaks.
 12. The polarizer of claim 11, wherein the light-transmissive inhibiting surface is disposed on one side of substantially all of the peaks.
 13. A filter, comprising: at least one subwavelength optical microstructure having at least a part of a surface covered with a light-transmissive inhibiting surface; and a resonance structure adjacent to the microstructure for reflecting light of a predetermined wavelength that has passed through the microstructure.
 14. A method of forming a polarizer, comprising: partially covering a subwavelength optical microstructure with light-transmissive inhibiting surface, wherein optical microstructure includes linear prisms; and disposing a coating over at least part of the optical microstructure and the metalized surface. 